The present invention relates generally to a virtual tape data storage arrangement, and more particularly to an improved method for selectively controlling reutilization of space occupied by expired data.
Generally, automated cartridge systems (ACS) provide a mechanism by which multiple users in a data processing system can have common access to multiple data storage subsystems such as magnetic tape cartridge devices. In conventional tape systems, data files generated by remote user computer systems for storage on a particular tape cartridge include a predetermined expiration date in the file meta data which is used as a control mechanism by which a tape management subsystem can determine whether a particular space on a tape can be rewritten with new data. However, in conventional tape systems, expired data from a xe2x80x9cscratchedxe2x80x9d tape volume is not actually deleted from the tape until a user actually writes new data to the tape. In other words, conventional tape systems conveniently provide a xe2x80x9csafety netxe2x80x9d for users who decide they still wish to be able to retrieve data from storage even though the data may be past the original expiration date.
Because conventional tape systems have proven to be quite inefficient in data storage space utilization, a virtual tape system has been developed which significantly improves storage space utilization and control by incorporating the advantages of an intermediate disk buffer as part of a tape emulation arrangement. Such an arrangement is taught in commonly owned copending U.S. patent application Ser. No. 09/110,217, filed on Jul. 6, 1998, now U.S. Pat. No. 6,094,605 and incorporated by reference herein.
More specifically, in the referenced virtual tape system, a disk buffer is connected between remote users and the tape storage devices and arranged to appear to users as though it were a physical tape device. All data volumes are initially stored in the disk buffer, and subsequently written to a physical tape device using predetermined protocols which limit the occurrence of unusable dead spaces on the tapes while also improving the ability to reclaim any fragmented space which does occur. In such a virtual tape system, a user reads and writes only to the disk buffer, but believes they are reading and writing to an actual physical tape device.
While efficiency in space management and utilization are significantly improved with the virtual tape system, users also lose the above-noted safety net feature inherently provided by conventional tape systems. More specifically, to achieve higher efficiency, the virtual tape system operates to automatically reutilize any tape and disk buffer space occupied by expired data without user action, i.e., a user does not have exclusive monopoly of a particular tape like in a conventional tape system because the tape can be reused any time a new data volume is received into the disk buffer. Emulating the safety net feature in the virtual tape system would involve prohibiting the reuse of any tape space until a user reuses a corresponding virtual tape volume name for the data volume stored in the space irrespective of whether the corresponding data has expired.
However, such an arrangement reintroduces significant inefficiency in storage space utilization and reclamation, thereby defeating a main advantage of the virtual tape system. As a result, a need exists for an improved method of controlling reutilization of data space in a virtual tape system which can provide a safety net for users while also minimizing the impact of such a feature on efficiency of data storage space utilization and management.
It is therefore an object of the present invention to provide an improved method for controlling reutilization of data space in a virtual tape system which allows a user to control whether space occupied by expired data can be automatically reused by a tape management system.
It is another object of the present invention to provide a method for controlling reutilization of data space in a virtual tape system which allows selective reuse of physical storage space occupied by a scratched virtual volume without waiting until a user actually reuses the virtual volume.
In accordance with these and other objects, the present invention provides a method for controlling reutilization of data space in a virtual tape system which allows a user to designate whether a particular data volume can be automatically deleted at the time of expiration without waiting for the user to actually reuse the virtual volume.
In accordance with one aspect of the present invention, a method is provided for selectively controlling reutilization of data space in a virtual tape system which includes selectively designating by a remote user whether a particular data volume file can be automatically deleted by the virtual tape system without any further action by the user after a predetermined expiration date for the data volume file has elapsed, detecting whether a data volume file has been designated by the user for automatic deletion, and prohibiting deletion from the virtual tape system of the stored data corresponding to a data volume based on whether the data volume file was designated by the user for automatic deletion. In accordance with another aspect, a predetermined grace period can be provided before automatic deletion is performed.
With such an arrangement, the present invention can allow a user to selectively xe2x80x9cprotectxe2x80x9d data past an original expiration date, while also allowing automatic reutilization of storage space for data which has not been specifically protected by the user.
These and other objects, features, and advantages of the present invention will be readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.